The NC Clean Energy Technology Center is collaborating with the NC Department of Environmental Quality (NC DEQ) on a project to analyze utility operating reserves to balance renewable solar photovoltaic (PV) generating facilities on the NC electric grid. The project aims to better understand the current needs for operating reserves due to solar PV grid integration, and to identify and evaluate feasible technology alternatives for power reserve requirements as the solar PV capacity in the state grows to meet demands for clean electricity.  

At a time when states are increasing their carbon emission reduction goals, plans to integrate larger amounts of renewables into the grid are becoming commonplace. For example, in North Carolina the Clean Energy Plan calls for a 70 percent power sector GHG emissions reduction below 2005 levels by 2030, Virginia’s Clean Economy Act requires the state’s largest utility to deliver 100% renewable electricity by 2045, and more recently in May 2021, Arizona extended and expanded the state RPS to 100 percent carbon-free electricity by 2070.  

There are a number of studies discussing the integration of renewables and their effect on the existing power grid. Due to the intermittency of solar and wind, grid operators require additional technologies to balance the grid and remain in compliance with NERC reliability standards. Utilities employ different types of reserves (contingency, flexible, regulating) to balance the grid and respond to changes in power demand and supply, whether they are caused by conventional or renewable generation. Depending on the need, different technologies such as natural gas or coal fired combined or simple cycle turbines, storage, demand side management, and market transactions, can be called on to provide the reserves. Of course, all of these technologies have their pros and cons anywhere from emissions, to cost, to availability. One issue with using fossil fuel generation for providing power reserves is the possible increase of emissions when these generators are operated below the optimum load levels. 

Intermittent generation in North Carolina is mostly related to solar PV, but there are ways to significantly reduce the effect of intermittency by making solar more flexible. A 2018 study by Energy and Environmental Economics prepared for Tampa Electric Company (TECO) showed that increasing the operating flexibility of solar could decrease unwanted curtailment and increase the economic value of solar. Adding battery energy storage to solar facilities is another way of smoothing output of solar PV facilities to the grid and increasing the value of solar energy. For example, the Virginia Clean Economy Act calls for Dominion to procure at least 2.7 GW of energy storage by 2035 to help balance intermittent generation. In 2019 the North Carolina Utilities Commission approved a System Integration Service Charge (SISC) that requires solar facilities that have uncontrolled output to the grid and that are “must take” generators (i.e. the utility must always accept the generated power and cannot curtail them). Solar facilities that can limit fluctuation by becoming “controlled” solar with energy storage integration, dispatchable contracts, or other mechanisms can avoid this charge.  Thus, increasing flexibility could help with grid balancing, avoid additional charges, and reduce the need for fossil-fueled reserves. 

This project, which will help identify and evaluate future needs and technology alternatives for power reserve requirements, is expected to be completed by December 2021.